This invention relates to continuous casting and, more particularly, to continuous casting of ferrous metals wherein the ferrous metal is continuously cast through a casting mold and withdrawn from such mold downwardly along an at least partly arcuate path and into a horizontal path.
Ferrous metals are continuously cast into strands by pouring hot, molten metal into the upper end of a mold and continuously withdrawing a metal strand from the bottom of such mold. As the molten metal passes through the mold, the surfaces of the metal contiguous to the mold walls are cooled, solidified and hardened to form a casing or shell of solidified metal around the molten metal in the strand. After leaving the bottom of the mold, the metal continues to cool and the casing or shell of solidified metal around the molten core thickens until the whole strand section is solidified.
The shell of solidified metal around the molten core, as the continuous cast strand leaves the mold, is relatively thin, fragile and requires support. Such support, in continuous casting of ferrous metals, is customarily provided by rolls which engage and support the opposite sides of the continuously cast strand. The supporting rolls immediately below the mold, where the shell of solidified metal round the strand core is thin, are usually of relatively small diameter and are longitudinally spaced closely together. To assist cooling of the slab and the thickening of the shell of solidified metal, such supporting rolls immediately below the casting mold may be liquid cooled. Further away from the mold bottom, where the metal has cooled and the shell of solid metal has thickened, rolls of larger diameter, spaced at greater longitudinal distance, are usually employed. To control the casting speed, certain of the supporting and guiding rolls may be driven.
In conventional continuous casting it is known to press guiding and supporting rolls with spring-load against stop means or directly against the strand surface. The disadvantage of such a solution is the increase in said spring-load because of perpendicular movement of said rolls by said strand. The differing restraining force prevails according to the characteristic line of the spring (spring constant) and usually is approximately proportional to the length of compression. Such an increase of the restraining force applied to the rolls is undesirable because the rolls are not protected against overload and roll damage will occur. Another disadvantage is the high cost of spring means directly acting at the support rolls of large slab casting machines, because the directly acting spring-load applied at the supporting rolls for the purpose of counteracting a ferrostatic pressure of about 10 meters height or more is very high.
Conventionally, in continuous casting, the opposing supporting and guiding rolls are divided into segments. The rolls are mounted on supporting elements. The supporting element carrying the rolls at one side of the strand is mounted in the segment for movement relative to the supporting element carrying the rolls at the opposite side of the strand in a direction normal to the strand casting axis. The distance between the supporting elements and opposing supporting rolls is usually adjusted by stops selectively inserted between the elements and by urging such elements into engagement with such stops. By changing the thickness of such stops, the cross section or thickness of the cast strand may be changed.
During normal casting operation, the elements are held in engagement with the stops so that the distance between the opposing supporting and guide rolls is maintained constant. This is accomplished by applying a restraining force of sufficient magnitude to the elements to maintain the supporting rolls in contact with the strand being continously cast. The magnitude of the restraining force applied to the elements should be so great that, on the one hand, the ferrostatic pressure is kept under control and, on the other hand, damage to the rolls, roll supports and segments will not result should abnormal casting conditions occur. For example, if the casting machine should be slowed down or stop, a breakout of the casting metal should start and heal over or, if for some other reason, there should occur a bulge or irregularity in the strand being cast, movement of the supporting elements and rolls to allow passage of the bulge or irregularity is desirable. Otherwise, there would be damage to the continuous casting apparatus. By permitting the supporting elements and rolls to open up while, at the same time, maintaining the rolls in supporting contact with the strand, integrity of the strand, particularly at the upper part of the path where the core is molten, can be maintained. The restraining force applied to the supporting elements and rolls which maintains the rolls in supporting contact with the strand being cast and which, at the same time, permits movement of opposing rolls away from each other, normal to the casting axis, should remain constant during such movement. Otherwise, unequal supporting forces will be applied to the strand and casting equilibrium would be disrupted. One means heretofore employed for applying such restraining force to the supporting elements and opposing rolls has been by hydraulic units mounted at the sides of the segments and interconnecting the elements.
One of the difficulties in using hydraulic units for applying restraining forces has been the failure of such units when a pressure failure occurs. Such pressure failure not only effects the elements at the unit causing such failure but also results in failure in all units connected thereto. Furthermore the hydraulic fluid required by such units is subject to combustion when leakage occurs and the resulting fire can cause extensive damage to the casting equipment. Hydraulic fluid leakage also results in contamination of the cooling medium used to cool the cast strand. Such contamination not only adversely effects the cooling but also cause damage to the cast strand.